Chirality and (Green) Life

Chirality of molecules describes the phenomenon when two molecules look almost identical but represent non-superposable mirror images, like the left and the right hand, why it is also called molecular “handedness”. Chirality plays a crucial role in the chemistry of life as many chiral molecules are almost exclusively found in one form but not in the other. A prominent example for such “homochirality” are amino acids as primary metabolites and building blocks of all proteins. In these contexts, they are just found in their L-form but not in their D-form. Nevertheless, it is often neglected in the textbooks that D-amino acids are regularly found in all kinds of organisms from bacteria to human beings. There, D-amino acids are essential elements of the bacterial cell wall, part of the human cerebrospinal fluid, or co-agonists of neurotransmitters. When it comes to plants, knowledge about D-amino acids was relatively scarce for a long time and they were supposed to be even inhibitory for plant growth. In the last years, this could be proven wrong, and there was growing evidence that plants possess a specific set of proteins to synthesize and metabolize D-amino acids. Furthermore, first physiological functions could be assigned to D-amino acids in plants with the aid of intracellular nanosensors. However, D-amino acids as small nanoobjects or as parts of larger nanostructures are an interesting showcase how small structural changes can lead to fundamental differences from structural recognition up to physiological functions in cells.

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